Most computers and portable electronic devices require power supplies that are capable of maintaining an output voltage within a specified range for a certain amount of time, typically 15 to 25 milliseconds, after an input voltage drops out. This time, referred to as the hold-up time, is used to orderly terminate the operation of a data processing equipment or to switch over to UPS operation after a line failure. The required energy to maintain the output voltage during the hold-up time is delivered from a properly sized energy-storage capacitor coupled to the input of the power supply.
In order to maximize the power density of the power supply, the size of the energy-storage capacitor needs to be minimized. U.S. Pat. No. 6,504,497, the content of which is herein incorporated by reference in its entirety, discloses an approach to maximize the utilization of the stored energy by using a hold-up time extension circuit. However, further improvement in the hold-up time extension circuit is needed.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.